Important Question About my Period?

Okay, so I was out, and I was driving up a mountain when I got a cramp. I went to the restroom and a little bit later, and I saw that my cycle had come on. So I put on a pad, and then I checked it a few hours later. It really hadn't done much. So, the next day I checked it again and it had done nothing since that previous afternoon. If this will help any, I have irregular periods. I also read that high altitudes can cause your period to start. Can anyone tell me what happened here. I'm pretty confused. Thanks!